1. Field of the Invention
The present invention relates to a toner used in a recording method utilizing electrophotography or the like.
2. Description of the Related Art
A large number of methods for electrophotography are known. An electrostatic latent image is formed on an electrostatic image bearing member (hereinafter, also referred to as “photosensitive member”) by generally utilizing a photoconductive substance and using various types of apparatus units. The latent image is then developed with a toner and made to be a visible image; and the resulting toner image is transferred on a recording medium such as paper as needed, and thereafter fixed on the recording medium by heat, pressure or the like to thereby obtain a copy. Image forming apparatuses using such electrophotography include copying machines and printers.
Shift from analog to digital is occurring in these printers and copying machines, and the image quality is demanded which is excellent in reproducibility of latent images and is of a high resolution while being stable also in long-term use. A toner good in fixing property is further demanded as an energy saving measure, and for the improvement in the fixing property, the improvement in a binder resin, the improvement in a wax and the like are being carried out.
Here, paying attention to a wax, it is generally known that the use of a wax in a large amount decreases the viscosity of a toner when it is melted and makes the fixing property of the toner good. The use of the wax in a large amount, however, is liable to make the durability and the preservability of the toner inferior, so the simultaneous satisfaction of the both has been attempted conventionally by adjusting the balance between the fixing property, and the durability or preservability.
Even in the range of simultaneously satisfying the both, however, a new bad effect on images such as the image density thinness or weakness at image ends comes to occur.
The density thinness at both ends of images occurs as follows. Many printers form electrostatic latent images on a photosensitive member surface by a laser using a scanner. Inside the scanner, the electrostatic latent image is formed by a polygon mirror rotating at a high speed, but the potentials at both ends of the electrostatic latent images drop due to a part of the polygon mirror being contaminated and the developing contrast is reduced to thereby cause the density thinness at both ends of the images.
An analysis of the contamination of the polygon mirror revealed that the contamination is caused by a wax component of a toner. It is known that whereas the wax oozes out in the fixing time of the toner and exhibits the release property from a fixing member, a part of the wax is volatilized. On the other hand, since the polygon mirror in the scanner interior rotates at a high speed, the scanner interior pressure becomes negative and the scanner interior is liable to draw in surrounding air. A part of the wax component volatilized and solidified is then drawn in the scanner interior and a part of the wax component deposits on the polygon mirror to thereby resultantly cause the density thinness at both ends of images as described above.
Many types of toners are proposed for the improvement in the fixing property, and in many cases a combination of two waxes (see Japanese Patent Application Laid-Open Nos. H08-050367 and 2006-243714), or a wax having a special composition (see Japanese Patent Application Laid-Open Nos. H11-133657 and 2007-193253) is used. However, although an improvement in the fixing property by the use of these proposed waxes is recognized, the waxes are insufficient for the density thinness at both ends of images caused by the polygon mirror contamination, and an improvement is demanded.